This invention relates to a gas chromatograph used for the analysis of various chemical substances and, more particularly, to a gas chromatograph provided with both a vaporization chamber for split analyses and another vaporization chamber for direct injection analyses such that selectably both split and direct injection analyses can be carried out.
Prior art gas chromatographs adapted to be used selectably for both split and direct injection analyses by switching flow routes are generally provided with, as shown in FIGS. 1A and 1B, a first flow route connected to a first vaporization chamber 3a for split analyses connected to a column 6a provided with a detector 7a and a discharge flow route 10 provided with a carrier gas discharge valve 5, and a second flow route connected to a second vaporization chamber 3b for direct injection analyses connected to another column 6b with a detector 7b, as well as a carrier gas supply route 2 including a carrier gas supply valve 1 for adjusting the flow rate of the carrier gas through a carrier gas supply route 2, a pressure sensor 4 and a switch valve 8 or 18 for selectably connecting the carrier gas supply route 2 to the vaporization chamber 3a for split analyses or the vaporization chamber 3b for direct injection analyses. When a split analysis is carried out, the carrier gas discharge valve 5 in the discharge flow route 10 is adjusted according to the output from the pressure sensor 4 in order to adjust the pressure inside the vaporization chamber 3a. When a direct injection analysis is carried out, the carrier gas supply valve 1 is adjusted according to the output from the pressure sensor 4.
When the prior art gas chromatograph shown in FIG. 1A is used for a split analysis, its switch valve 8 is in the position indicated by solid lines in FIG. 1A such that the carrier gas is introduced into the vaporizer chamber 3a for split analyses, a portion of it being discharged through the discharge flow route 10 and the rest being led into the column 6a. In the meantime, the carrier gas discharge valve 5 is controlled by the output from the pressure sensor 4 such that a desired proportion of the carrier gas supplied through the carrier gas supply valve 1 will be discharged. It will be assumed that the flow resistance between the pressure sensor 4 and the carrier gas discharge valve 5 is small enough to be negligible. When this chromatograph is used for a direct injection analysis, on the other hand, the switch valve 8 is switched to the position indicated by dotted lines in FIG. 1A such that the carrier gas supplied through the carrier gas supply valve 1 is introduced entirely into the vaporization chamber 3b and from there into the column 6b for direct injection analyses. The carrier gas supply valve 1 is controlled in this case by the output from the pressure sensor 4, but an accurate control becomes difficult due to a temporal phase difference which occurs between the action of the carrier gas supply valve 1 and the pressure change detected by the pressure sensor 4 because of the flow resistance inside the carrier gas supply route 2 and the direct injection flow route (indicated by numeral 12) between the switch valve 8 and the vaporization chamber 3b as well as the volume of the vaporization chamber 3b.
The prior art gas chromatograph shown in FIG. 1B is different in that its pressure sensor 4 is inserted on the upstream side between the carrier gas supply valve 1 and its switch valve 18. When this gas chromatograph is used for a direct injection analysis, its switch valve 18 is set as shown by a dotted line such that the carrier gas flows entirely through the vaporization chamber 3b into the column 6b for direct injection analyses. There is no problem in this situation because the carrier gas supply valve 1 is controlled by the output from the pressure sensor 4. When this gas chromatograph is used for a split analysis, on the other hand, the switch valve 18 is set as shown by the solid line in FIG. 1B such that the carrier gas is introduced into the vaporization chamber 3a for split analyses and the carrier gas discharge valve 5 is controlled by the output from the pressure sensor 4. In this situation, however, an accurate control becomes difficult due to a temporal phase difference which occurs between the action of the carrier gas discharge valve 5 and the pressure change detected by the pressure sensor 4 because of the flow resistance inside the carrier gas supply route 2, the split flow route (indicated by numeral 14) and the discharge flow route 10 as well as the volume of the vaporization chamber 3a.
Prior art gas chromatograph apparatus for both split and direct injection analyses were formed as shown either in FIG. 1A or in FIG. 1B. Thus, either the control in direct injection analyses or control and accuracy in split injection analyses had to be compromised if use is made of a prior art gas chromatograph as described above.